1) Field of the Invention
This invention relates to a method for the rapid production of insulated glass units, and in particular to the accelerated heat bonding or curing of the edge sealants of such units.
2) Description of the Prior Art
In a conventional insulated glass unit, two sheets of glass are placed parallel to one another with a small gap therebetween, this gap being maintained by longitudinal spacers between the sheets positioned Just inside the peripheral edges of the sheets. The spacers generally contain a desiccant which is in communication with the gap between the glass sheets to absorb residual moisture. A liquid sealant such as a polysulphide, polyurethane or silicone sealant is then applied around the outside of the spacer between the peripheral edges of the sheets to seal the unit. These sealants are typically two-component systems, the base and the curing agent being mixed just prior to application to the glass.
More recently, integral sealing strips have been developed which comprise for example an extrusion of "hot melt butyl" which may incorporate a desiccant and optionally also a spacer, suitably in the form of an aluminum strip. Such strips can be supplied in rolls, stored in airtight containers.
In the manufacture of such units the sealant may require a long cure time, typically 2 to 4 hours, before the unit can be passed on to the next manufacturing stage. This creates particular problems in a continuous production line process since units have to be removed from the production line and stood for several hours. There arises the further possibility with liquid sealants that these may tend to flow during this cure period, particularly since the insulated glass (IG) units are generally in a vertical position during curing. Also, if a sealant system with a fast cure (and hence a short pot life) is used difficulties will arise if there is any delay in the IG unit production line.
One way of overcoming this difficulty has been to use one part hot melt sealant systems, such as the hot melt butyl strips discussed above, instead of the conventional two part systems which cure at room temperature. Hot melt systems however require high temperature and pressure to effect adhesion.
There is therefore a need for a method of putting energy into the chemically curing sealant to accelerate the cure. Straightforward heating in a hot air oven is however unsatisfactory since this also results in heating of the air in the cavity between the glass sheets which therefore has to be vented. Such heating also increases the temperature of the whole unit, including for example plastics spacers and corner pieces, which can also cause problems. The use of direct infra-red radiation also causes heating and expansion of the air in the cavity.
It is known from the prior art that microwave energy can be used to accelerate the curing of some polar resins. U.S. Pat. No. 4,011,197 discloses the microwave curing of organosiloxane compositions and U.S. Pat. No. 3,936,412 discloses microwave curing of thermoserring sealants such as polysulphides and polyurethanes.